1. Field of the Invention
The present invention relates to a liquid-crystal optical element used as an aberration correcting optical element for aberration correction for information recording and reproduction using an information recording medium, such as a variable-focus lens of a digital camera, optical disc, etc., a camera using the liquid-crystal optical element as a lens, and an optical pickup device using the liquid-crystal optical element.
2. Description of the Related Art
A conventionally known liquid-crystal optical element, such as the one shown in FIGS. 19A and 19B, is used as an aberration correcting optical element for aberration correction for information recording and reproduction using an information recording medium, such as a variable-focus lens of a digital camera, optical disc, etc.
FIGS. 19A and 19B are a plan view and a sectional view, respectively, showing principal electrodes of the liquid-crystal optical element. A liquid crystal layer 11 is sandwiched between an upper glass 12 and a lower glass 10. A whole-surface electrode 132 is provided on the upper glass 12, while a plurality of transparent electrodes 120, 122 and 124 are arranged concentrically on the lower glass 10. In this liquid-crystal optical element, voltage applied to the concentric transparent electrode group is changed to differentiate the respective optical refractive indexes of the affected parts of the liquid crystal layer 11. Thus, the liquid-crystal optical element is used as a variable-focus lens or an aberration correcting optical element.
In the liquid-crystal optical element described above, as shown in FIG. 19A, however, the ring-shaped segment electrodes 120, 122 and 124 that are arranged concentrically constitute one transparent electrode layer. Therefore, it is necessary to provide clearances 126 and 128 between the ring-shaped segment electrodes and draw out a wire group 130 for connection with a drive section to a glass end portion. Thus, if the liquid-crystal optical element is used as a camera lens, image distortion is caused in regions corresponding to the clearances 126 and 128 and the wire group 130. If the optical element is used as an aberration correcting optical element, on the other hand, an information recording or reproduction error is inevitably caused owing to a failure of aberration correction. These problems have become serious with the increase of the number of pixels of digital cameras and the density of information recording media.
In an example of the liquid-crystal optical element for aberration correction (e.g., Japanese Paten Application Laid-Open No. 2001-176108), therefore, two transparent electrode layers are arranged such that a first one of them is provided with a group of first ring-shaped segment electrodes arranged concentrically, and a second layer with a group of second ring-shaped segment electrodes that fill clearances between the first segment electrodes. In this example, the same driving voltage for the first segment electrodes that adjoin the second segment electrodes for clearance fulfillment in plan is applied to the second segment electrodes. By doing this, the accuracy of aberration correction in the clearances 126 and 128 between the concentric segment electrodes shown in FIG. 19A is improved.
Even in this example, however, the wire group 130 for connection shown in FIG. 19A cannot achieve aberration correction, and the problem of image distortion still remains. In consequence, this example cannot display its properties as an aberration correcting optical element for high-density information recording media or as a digital camera lens.